1、(8xy-x²+y²)-(x²-y²+8xy)=[8xy-(x²-y²)][8xy+(x²-y²)]
=64x²y²-(x²-y²)=64x²y²-x^4+2x²y²-y^4=66x²y²-x^4-y^4
2、 (2x²-1/2+3x)-4(x-x²+1/2)= 2x²-1/2+3x-4x+4x²-2
= 6x²-x-2.5
3、3x²-[7x-(4x-3)-2x²]=3x²-7x+(4x-3)+2x²
=5x²-7x+4x-3=5x²-3x-3